For integrated circuit power devices that experience high currents, e.g., currents above about 100 milliamps, thick copper is desirable for forming low resistance leads. Where the currents are above about 1 amp, and especially when the currents are above about 10 amps, thick copper can be considered essential. Thick copper allows the higher currents to be carried in a considerably smaller area than would be required with other metal layers. Thick copper is formed over a protective overcoat. The protective overcoat provides physical, chemical, and ion protection for underlying structures.
According to a standard process for forming thick copper leads, the protective overcoat is lithographically patterned to expose the bond pads. The bond pads are typically about 60 μm to about 100 μm square. A conductive barrier layer and a copper seed layer are sputter deposited over the protective overcoat and within the openings patterned through the overcoat. A resist coating is then formed and patterned to cover the copper seed layer everywhere except where thick copper is desired. Thick copper is then plated on the surface. After plating, the resist is removed and exposed portions of the barrier layer and seed layer are etched away using a wet etchant. This process is generally effective, but the resulting products in some cases may show undesirable failure rates, especially in next generation devices.
Accordingly, what is needed in the art is an improved interconnect lead and a method of manufacture therefor.